The present invention relates to the manufacture of bags or pouches of synthetic foils, and more specifically, to bags, or pouches of this type which, even if filled with material capable of flowing, such as liquid or granular material, are able to stand up reliably or be self-supporting. The term "synthetic foil" used hereafter includes all synthetic foils customarily used for producing bags, including mono-foils of sealable material, multiple foils with at least one sealable plastic layer, a variety of compound foils with at least one sealable synthetic layer, as well as metallized synthetic foils.
In recent years, bottles, boxes or cannisters have been replaced increasingly by flat-bottom bags that are self-supporting and are made from bendable or flexible synthetic foils. When producing such bags one starts for instance with a bag having a seamless bottom and an open top. This bag is grasped at two opposite flat sides and is spread such that at its lower part a bottom surface and two triangular tip portions are created which protrude outwardly. The tip portions are essentially compressed in the plane of the bottom surface and are provided with a welded seam in the areas immediately adjacent the rectangular bottom surface. In one example illustrated in U.S. Pat. No. 3,435,736, this welded seam extends over the entire area of the tip portion and closes the same completely. According to another example in U.S. Pat. No. 4,041,851 the welded seam of the tip portion is limited to a strip-like area in the immediate vicinity of the bottom surface. Upon completion of the welded seam the tip portions are, along the crease or fold line extending immediately adjacent the bottom surface of the bag, folded against the under side of the bottom surface, and are connected to the surface. When using these known bags for packing liquids, especially for larger quantities, experience has shown that the ability of the bag to stand up or be self-supporting is insufficient. The liquid inside the bag brings about a bulging deformation of the bendable synthetic foil even at the supporting surfaces proper, and thereby lifts the supporting surfaces at the sides. When the approximately triangular tip portions are folded back onto the bottom side of the bottom surface the available supporting surface of the bag is reduced even more and the ability of the bag to stand up is impaired accordingly.
A somewhat better support of the bag results if the tip portions are cut off with the exception of the bottom welded seam adjacent the bottom surface of the bag and if they are left to protrude at an angle outwardly without being folded. In this way, however, the tightness of the bag and the stability in the bottom area is diminished. Such a bag cannot be maintained sufficiently tight for packing liquids, by means of a simple sealing seam along the two cut-off tip portions located opposite each other. The two bottom-welded seams adjacent the bottom welded surface have to be overwelded for a sufficiently tight seal, especially for liquids. This requires an additional manufacturing step, which is described in U.S. Pat. No. 4,041,851 (Jentsch).
It is, therefore, an object of the present invention to provide a flat-bottom bag made of synthetic foil, which is capable of standing up much better compared to similar bags heretofore available and which has an optimum tightness and stability in the area of the bottom. The high self-supporting capability of the bag and optimum tightness and stability thereof in the bottom area are to be accomplished with a minimum of manufacturing expense.